1. Field of the Invention
The present invention relates to high-frequency switch modules in which a plurality of communication signals are transmitted and received using a common antenna.
2. Description of the Related Art
To date, various types of high-frequency switch modules have been devised in which a plurality of communication signals using different frequency bands are transmitted and received using a common antenna. In such high-frequency switch modules, a switch device made of a semiconductor, such as an FET, performs switching among communication signals or switching between a transmission signal and a reception signal of one type of communication signal.
In the case where such a switch device is used, when a high-power signal such as a transmission signal is input to the switch device, high-order harmonics, such as a second harmonic having a frequency twice the fundamental frequency and a third harmonic having a frequency three times the fundamental frequency may be generated due to distortion in the switch device. Such high-order harmonics generated in the switch device are output from all the terminals of the switch device to the outside. There may be a case in which high-order harmonics output to a transmission signal input circuit side are reflected by a filter connected to the transmission signal input circuit side of the switch device, transmitted again through the switch device, and radiated from an antenna.
Hence, in Japanese Unexamined Patent Application Publication No. 2004-173243, a phase shifting unit is connected between a switch device and a low pass filter of a transmission signal input circuit. With this configuration, by making a harmonic signal reflected by the low pass filter and output to an antenna side through a switch IC and a harmonic signal directly output to the antenna from the switch device have a phase difference of 180°, these harmonic signals cancel each other out.
However, with the configuration illustrated in Japanese Unexamined Patent Application Publication No. 2004-173243, a phase shifting unit needs to be provided between the switch device and the low pass filter and, hence, the number of constituent components of the high-frequency switch module is increased, resulting in an increase in size. Further, since a phase shift applied by the phase shifting unit is determined by the length of an electrode forming the phase shifting unit, a high precision electrode pattern needs to be formed. On the other hand, when the precision with which the electrode pattern is formed is low, the effect of attenuating a harmonic signal is significantly reduced.